An important additional dynamic is that in the 1910s the Europeans made conflicting agreements with nationalistic groups of Jews and Arabs that each of them could have the colonial land once it was independent. The Europeans created the countries of Israel and Jordan at the same time, more or less, next to each other, with the idea that people would be moved around so Jews and Arabs could split the area, but neither side got what it was promised, and it created a lot of refugees.

This was a naive idea and the two new countries, plus their neighbors, were almost immediately at war. Those wars have been pretty consistent since the colonial empires left and every country in the area has a mix of millions of refugees from the other countries nearby living in it.

It was a European solution based on what had sort of worked in Hungary that was totally oblivious to the reality on the ground in the middle east, and since then it's a question of everybody rightfully feeling that they are a hair's breadth away from being dispossessed or murdered, so further sorts of internationally facilitated sharing agreements haven't really resolved much. And which grievance you think is most righteous or most important is mostly a product of perspective, bias or propaganda.